A method has been proposed for manufacturing a compact optical nonreciprocal element by forming a waveguide on an Si layer of an SOI substrate, and bonding a magneto-optical material layer, which causes a light propagating in the waveguide to generate a nonreciprocal phase change, onto the Si layer. For example, Non-Patent Document 1 discloses a method for manufacturing an optical nonreciprocal element by bonding magnetic garnet by direct bonding (wafer bonding) onto an Si waveguide layer on which a rib waveguide is formed.    [Non-Patent Document 1] Hideki Yokoi and two others, “Si Dohaso o Yusuru Hi Sohan Soshi”, IEICE Technical Report, February 2004, Vol. 103, No. 667 (20040213), pp. 17-22